Multiplexer-demultiplexer module having an arrayed waveguide grating

ABSTRACT

In an optical module comprising an arrayed waveguide grating multiplexer-demultiplexer component having at least one inlet waveguide and at least one outlet waveguide, the module is integrated and comprises at least one inlet optical fiber and at least one outlet optical fiber, said inlet waveguide presenting an optical coupling interface with the inlet optical fiber and said outlet waveguide presenting an optical coupling interface with the outlet optical fiber, and a thin film filter is inserted directly at the optical coupling interface between the inlet and/or outlet waveguide(s) of the multiplexer-demultiplexer component and the inlet/outlet optical fiber(s) of the module.

[0001] The present invention relates to the field of wavelengthmultiplexer-demultiplexer components, and more particularly to arrayedwaveguide grating (AWG) multiplexer-demultiplexers. Such components areconventionally used in multiplexing and/or demultiplexing applicationsor for wavelength selection applications known as add and dropmultiplexing.

BACKGROUND OF THE INVENTION

[0002]FIG. 1 is a diagram of a conventional AWG component 20 integratedon a substrate 10, e.g. a silicon substrate. Inlet waveguides 11 conveylight signals at given wavelengths λ₁, λ₂, . . . λ_(n) into an inletcoupler 12 leading to an array of waveguides 13. The light signals aresubjected to phase shifts in the array of waveguides 13 and aresubsequently focused by an outlet coupler 14 into outlet waveguides 15.Each optical signal is subjected to the following operations:

[0003] diffraction in the inlet coupler 12 which is representedmathematically by the Fourier transform of the signal being diffracted,each waveguide of the array 13 situated at the outlet surface of thecoupler 12 receiving a fraction of the diffracted wave;

[0004] phase shifts in the array of waveguides 13 which are of variousoptical path lengths, with the optical path followed in any onewaveguide of the array being expressed as a function of the refractiveindex of the waveguide and as a function of its length; at the outletfrom the array of waveguides 13, these phase shifts give rise tointerference which is constructive in some particular direction thatdepends on wavelength; and

[0005] focusing the constructive interference of waves coming from thearray of waveguides 13 onto the outlet surface of the coupler 14.

[0006] Such an AWG is not capable on its own of performing wavelengthfiltering.

[0007] Japanese patent application No. 11 006 928 discloses an AWGassociated with components each comprising a thin film filter.

[0008] Such thin film filters are known and are made up of a successionof thin films having different refractive indices. The thin film filtersdisclosed in that document are of the band-pass type and they aretherefore suitable for eliminating undesirable wavelengths, specificallyfor the purpose of avoiding inter-symbol mixing or “crosstalk”.

[0009] The thin film filter components are interposed in the outletwaveguides from the AWG, thereby giving rise to additional optical loss.

[0010] In addition, in order to receive those components, the AWGsubstrate has trenches. Inserting components in that way gives rise tomanufacturing problems and to reliability problems.

OBJECT AND SUMMARY OF THE INVENTION

[0011] The object of the invention is to provide an optical moduleincluding an AWG component and a thin film filter that is capable,depending on the application, of processing wavelengths (or channels)individually or in given spectrum bands, with the module also providinghigh performance, being reliable, compact, and integrated.

[0012] To this end, the present invention provides an optical modulecomprising:

[0013] an arrayed waveguide grating multiplexer-demultiplexer component,said multiplexer-demultiplexer component comprising at least one inletwaveguide and at least one outlet waveguide; and

[0014] a thin film filter;

[0015] wherein the module is integrated and comprises at least one inletoptical fiber and at least one outlet optical fiber, said inletwaveguide presenting an optical coupling interface with the inletoptical fiber and said outlet waveguide presenting an optical couplinginterface with the outlet optical fiber; and

[0016] wherein said thin film filter is inserted directly at the opticalcoupling interface between the inlet and/or outlet waveguide(s) of themultiplexer-demultiplexer component and the inlet and/or outlet opticalfiber(s) of the module.

[0017] Unlike the prior art, the thin film filter of the invention isnot contained in an additional component that is added to the module.

[0018] In embodiments, the thin film filter is deposited on the couplingfacet of the inlet and/or outlet optical fiber(s) of the module, or onthe coupling facet of the inlet and/or outlet waveguide(s) of thecomponent.

[0019] The coupling facet thus acts as a substrate for the thin filmfilter of the invention.

[0020] According to a feature, the optical coupling interfaces betweenthe inlet and/or outlet waveguide(s) of the multiplexer-demultiplexercomponent and the inlet and/or outlet optical fiber(s) of the module areadhesive interfaces.

[0021] In an advantageous embodiment, the AWG multiplexer-demultiplexercomponent is integrated on a monolithic substrate and the optical moduleis integrated on a hybrid substrate.

[0022] In a first preferred embodiment, said thin film filter issuitable for selecting a single diffraction order from the outlet signalof said component.

[0023] A direct consequence of the optical signals diffracting in thearray of waveguides in a conventional AWG is that the spectrum of eachoptical signal in the outlet waveguides is reproduced over differentorders of diffraction. The phase shifting introduced by the array ofwaveguides is limited to modulo 2π.

[0024] Thus, as shown in FIG. 2, for a 16-channel demultiplexer theinlet signals can be transmitted in demultiplexed form at the outletover a plurality of diffraction orders at a wavelength intervalcorresponding to a parameter of the AWG known as the free spectral range(FSR). This parameter represents the spectral spacing between twosuccessive diffraction orders and depends on the hardware properties ofthe AWG, and in particular on the geometry of the couplers 12 and 14.

[0025] Unfortunately, this repeating of the optical spectrum can be adrawback in certain applications. In particular, when different signalsconveying different data propagate at respective wavelengths correspondto λ₁+FSR and to λ₁, and when these signals are demultiplexed anddelivered to the same outlet waveguide.

[0026] Thus, the spectral response of the thin film filter of theinvention is advantageously adjusted to allow only one diffraction orderto be output from the AWG. In this first embodiment, the other ordersare eliminated, i.e. they are not reused.

[0027] By way of example, starting from an inlet signal made up ofwavelengths in two transmission bands C (1530 nanometers (nm) to 1560 nmapproximately) and L (1565 nm to 1610 nm, approximately) the moduledemultiplexes and passes only those wavelengths that lie in band C.

[0028] In a second preferred embodiment, said thin film filter issuitable for allowing a group of wavelengths to be forwarded and issuitable for reflecting distinct wavelengths of said group ofwavelengths.

[0029] For example, starting from an inlet signal made up of wavelengthsin one of the transmission bands C and L, the module will demultiplexand pass only a group of wavelengths in said band C or L, e.g. four oreight wavelengths in a common sub-band, and it will reflect the otherwavelengths so that they can be reused. By way of example, these otherwavelengths are redirected by means of an optical circulator placedupstream of or integrated in the module of the invention.

[0030] Depending on the application, the optical module is a wavelengthmultiplexer-demultiplexer module and/or an optical module for wavelengthselection.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The features and advantages of the present invention appear moreclearly on reading the following description given by way ofnon-limiting illustration, and made with reference to the accompanyingfigures in which:

[0032]FIG. 1, described above, shows the conventional structure of anAWG multiplexer-demultiplexer;

[0033]FIG. 2, described above, is a diagram showing the demultiplexingspectrum from an AWG multiplexer-demultiplexer; and

[0034]FIGS. 3a and 3 b are diagrams showing possible implementations ofa preferred embodiment of the invention.

MORE DETAILED DESCRIPTION

[0035] The invention proposes making an integrated optical moduleincluding both an AWG multiplexer-demultiplexer component and a thinfilm filter, serving to pass a signal to its outlet only for certainwavelengths of inlet signal.

[0036] Such an optical module comprises at least one inlet optical fiber(a plurality if it is a multiplexer) and at least one outlet opticalfiber (a plurality if it is a demultiplexer), these optical fibers beingcoupled to an AWG multiplexer-demultiplexer component.

[0037]FIGS. 3a and 3 b are diagrams showing the inlet and outlet opticalcoupling interfaces in a preferred embodiment of the invention.

[0038] As described above, the AWG 20 has at least one inlet waveguide11 presenting an optical coupling interface with an inlet optical fiber8, and at least one outlet waveguide 15 presenting an optical couplinginterface with an outlet optical fiber 8′.

[0039] Such optical coupling interfaces are generally secured byadhesive. The optical fibers 8, 8′ are circular in section whereas thewaveguides 11 and 15 of the AWG are rectangular in section. In addition,since the AWG component 20 is monolithically integrated on a substrate10, welding is consequently difficult to implement.

[0040] The invention proposes inserting a thin film filter 5 directly inthe optical coupling interface between the inlet optical fiber 8 or theoutlet optical fiber 8′ and the inlet waveguide 11 or the outletwaveguide 15 of the AWG.

[0041] Thin film filters comprise a succession of thin films havingdifferent refractive indices that are deposited by vacuum spraying orevaporating using techniques that are well understood by the personskilled in the art. By varying the number, the thickness, and therefractive indices of the superposed layers, it is possible to determinethe spectral response of the filter: the thin film filter 5 is designedso as to be able to select the appropriate diffraction order of theoutlet signal from the AWG component.

[0042] In a variant, the thin film filter is designed so as to allow agroup of wavelengths to be passed while reflecting wavelengths that donot form part of said group of wavelengths.

[0043] The thin film filter 5 is advantageously deposited on thecoupling facet of the inlet or outlet optical fiber(s) 8 or 8′ of themodule. The coupling facet of an optical fiber is often cleaved andgenerally carries antireflection treatment implemented using a thin filmdeposition technique identical to that described for making a thin filmfilter.

[0044] Nevertheless, as shown in FIG. 3b, the thin film filter 5 couldalso be deposited on the coupling facet of the inlet or outletwaveguide(s) 11 or 15 of the component 20.

[0045] The thin film filter 5 is not contained in a component that isseparate from the module of the invention since it is directlyintegrated in the inlet or outlet optical coupling interface. Thus,since the AWG is integrated on a monolithic substrate, hybridintegration with inlet and outlet optical fibers serves to provide theintegrated module of the invention.

What is claimed is:
 1. An optical module comprising: an arrayedwaveguide grating multiplexer-demultiplexer component, saidmultiplexer-demultiplexer component comprising at least one inletwaveguide and at least one outlet waveguide; and a thin film filter;wherein the module is integrated and comprises at least one inletoptical fiber and at least one outlet optical fiber, said inletwaveguide presenting an optical coupling interface with the inletoptical fiber and said outlet waveguide presenting an optical couplinginterface with the outlet optical fiber; and wherein said thin filmfilter is inserted directly at the optical coupling interface betweenthe inlet and/or outlet waveguide(s) of the multiplexer-demultiplexercomponent and the inlet and/or outlet optical fiber(s) of the module. 2.An optical module according to claim 1, wherein the thin film filter isdeposited on the coupling facet of the inlet and/or outlet opticalfiber(s) of the module.
 3. An optical module according to claim 1,wherein the thin film filter is deposited on the coupling facet of theinlet and/or outlet waveguide(s) of the component.
 4. An optical moduleaccording to claim 1, wherein the optical coupling interfaces betweenthe inlet and/or outlet waveguide(s) of the multiplexer-demultiplexercomponent and the inlet and/or outlet optical fiber(s) of the module areadhesive interfaces.
 5. An optical module according to claim 1, whereinthe AWG multiplexer-demultiplexer component is integrated on amonolithic substrate.
 6. An optical module according to claim 1, theoptical module being integrated on a hybrid substrate.
 7. An opticalmodule according to claim 1, wherein said thin film filter is suitablefor selecting a single diffraction order from the outlet signal of saidcomponent.
 8. An optical module according to claim 1, wherein said thinfilm filter is suitable for allowing one group of wavelengths to betransmitted and is suitable for reflecting wavelengths that do not formpart of said group of said wavelengths.
 9. An optical module accordingto claim 1, constituting a wavelength multiplexing/demultiplexingoptical module.
 10. An optical module according to claim 1, constitutinga wavelength selection optical module.